1. Field of the Invention
The present invention relates generally to improvements in or relating to the treatment of waste or refuse materials for the recovery of useful gases therefrom. More particularly, the present invention relates to the process for the recovery of useful gases from waste materials by pyrolysis or similar thermal decomposition methods, in which the comminuted material is introduced into a heated, gastight drum or vessel for the production of the gases. Residual substances, such as ashes and other particulate materials, are separated from the gas and the latter is treated in a gas converter in the presence of air and heat for the production of combustion gases. The present invention also relates to the apparatus for carrying out the method of the invention.
2. Description of the Prior Art
A method for treating waste materials and the apparatus therefor have been described in German Pat. No. 2 432 504. In general terms, during the pyrolysis of waste, for example household garbage, industrial wastes and the like, the contained organic components are volatilized and degassed. The recovered gas is then further treated in additional steps to such an extent that it is useful in the operation of gas turbines and gas motors. Similarly, the gas may be of use in chemical operations as synthesis gas for new products, or for the utilization of the calorific value, as by-pass in boiler installations, or in the operation of large heating plants.
The production of such gases is normally by means of a horizontally disposed vessel or treatment drum which is rotating about its longitudinal axis which is slightly inclined with respect to the horizontal. The reactor, or drum, is gastight, and the operating temperature in it is maintained over the range of from about 450.degree. to about 600.degree. C., under the exclusion of oxygen and using indirect heating. The hitherto known processes normally used shredded wastes as the feed material. The gastightness was achieved by a corresponding valve means at the two ends of the drum, which therefore was generally operating in a discontinuous or batch manner. At the temperatures mentioned above, a complete decomposition is achieved of even the most difficult to treat materials when oxygen is substantially excluded. The remaining residue is comprised of ashes, metals, glass, degassed wood and coal residues, the so called low-temperature coke.
The gases won in this processing are subsequently treated in a gas converter or similar reactor. This processing may include partial combustion to heat the gas to a cracking temperature in the range of from about 1100.degree. to about 1200.degree. C. During cracking the long-chain hydrocarbons are converted to methane and hydrogen, and other simple hydrocarbons. Simultaneously, there is achieved a partial separation of the water, contained in the vapor phase in the gas mixture, into hydrogen and oxygen. During dissociation the gases are passed through a bed of hot coal in which the further reactions occur. The resulting gas mixture exits from the converter and is usually used after leaving a gas cooling and purification system.
The pretreatment and introduction of the waste materials into the reactor drum, and the removal of residues therefrom, has often lead to difficulties and was otherwise not satisfactory. Thus, heretofore, the collected wastes were roughly comminuted in a shredder and then conveyed to a storage by a belt conveyer. In conformity with the requirements at hand, the comminuted waste was then introduced from a large hopper into the treatment vessel, with the end of the hopper enclosing in an airtight manner the end of the treatment vessel. A considerable disadvantage of the known process resides therein that due to the moisture content in the waste a considerable amount of water is produced. This water is generally separated in the cooling and purification stage. The amount of water may be in excess of 0.5 m.sup.3 per ton of waste. Because the waste water contains an appreciable amount of deleterious substances, a cost-intensive purification is necessary. Furthermore, due to the high water content in the waste, a high energy input is required for the thermal processing, so that, in general, continuous indirect heating of the reactor drum will be required in order to maintain the desired conditions.
A further disadvantage of the known processes and apparatuses resides therein that decomposition of the material takes place during the intermediate storage of the shredded waste, and valuable energy stored in the material is then lost during extended periods of storage.
It is further of disadvantage in the known apparatuses that the waste may contain lengthy and spinning-prone substances, such as nylon stockings, ropes, synthetic/plastic strips, and the like. Such materials will disrupt the operation because they will get caught in feeder parts and on rotating parts. The removal of residues from the drum is also difficult in the known apparatuses. These residues are produced at a temperature in the range of from about 450.degree. to about 600.degree. C., and they are more or less bone-dry. Because they are difficult to transport in this state, there arises the need to moisten such residues, so that they will not become an environmental concern during transport or in storage, due to their capability to be easily carried by wind and air.